Minimum postmortem interval estimation using the development and gene expression patterns of Hemipyrellia ligurriens (Wiedemann, 1830) (Diptera: Calliphoridae) in Southern China

The developmental patterns of the oldest developing flies are commonly used by forensic entomologists to estimate the minimum postmortem interval (PMImin). Hemipyrellia ligurriens (Wiedemann, 1830) (Diptera: Calliphoridae) are widely distributed in the Australian and Palearctic regions and are closely associated with human corpses. Here, the developmental pattern of H. ligurriens was studied under laboratory conditions at 7 different constant temperatures between 16 and 34 °C. Five models were established for the study of H. ligurriens, including an isomorphen diagram, an isomegalen diagram, a linear thermal summation model, a nonlinear SSI model, and a logistic model. The lower developmental threshold and thermal summation constant of H. ligurriens evaluated by the linear thermal summation models were 8.99 °C and 4,967.35 degree hours, respectively. The lower developmental threshold, intrinsic optimum temperature, and upper lethal developmental threshold obtained by Optim SSI models were 12.56, 19.91, and 33.21 °C, respectively. The expression levels of 5 genes (Hsp83, Hsp60, USP, wg, and amKI) were analyzed at sequential developmental time points to estimate the pupal formation time of H. ligurriens under constant temperatures of 16 and 25 °C, and to verify the temporal regularity of this process. This study provides a foundation for forensic entomologists to accurately estimate the PMImin using H. ligurriens in future death investigations.